Deploying heterogeneous networks, where macro networks are complemented with small cells, is one way to improve capacity and coverage of the mobile network.
FIG. 1 illustrates a heterogeneous network comprising a macro cell 12, a small cell 14, a base station 16 of the macro cell 12, as well as a base station 18 of the small cell 14. Small cells are deployed where coverage and capacity of a macro network needs to be improved.
One way to deploy a heterogeneous network is to use a base station architecture based on remote radio equipment and radio equipment controllers. The remote radio equipment comprises radio frequency generation means and antenna elements whereas the radio equipment controller typically comprises baseband signal processing means. The remote radio equipment and radio equipment controller are typically interconnected by means of fibre carrying digital baseband signals, such as user plane information of in-phase and quadrature modulation data, so called IQ data.
This approach enables common baseband signal processing means to be used for macro and small cells. As a result, antennas at different macro and small cell sites can be configured to synchronously transmit a single logical cell identity and other common control information, together forming one logical cell or, differently worded, a combined cell.
FIG. 2 schematically illustrates a heterogeneous network comprising logical cell 22, a base station from the macro cell 24 and the base station 26 from the small cell in the combined logical cell. Wireless devices located within the logical cell are denoted by 28.
The removal of cell borders of small cells under the coverage of the macro cell has positive mobility effects, since it reduces handover signaling and handover interruption as well as the risk of other connection disturbances. In addition, inter-cell interference between small cells and a macro cell of a combined cell will no longer be a problem and can be managed more efficiently with common baseband processing means though interference mitigation features, such as, coordinated multipoint reception and transmission. Small cells are accordingly coordinated with the macro cell of the combined cell.
Using a logical cell hence requires that connected macro and small cells share baseband signal processing means. Examples of baseband signal processing means are baseband processing unit and radio equipment controller.
In practice, there is a limit on the number of radio equipment that can be connected to the one and the same radio equipment controller or a group of radio equipment controllers. The delay difference between any two cells forming one logical cell must be below a threshold time duration, in order not to risk that a synchronization requirement cannot be fulfilled. Noncompliance with this requirement causes interference within the logical cell.
Moreover, there can also be an upper limit within the radio equipment controller on how many cells can be grouped into one logical cell. This is due to hardware and/or software limitations, such as processing power, memory accessibility, interconnection interface speed within the logical cell, etc.
One problem is hence to determine which remote radio equipment to share the same radio equipment controller, being an example of baseband signal processing means, in order to create a single logical cell.
This task is not trivial and has no obvious solution.
There is hence a need for an inventive method for defining logical cells.